Importing time-dependent mesh
You can use the NewTek MDD and PC2 formats (though you may have to enable their separate addons in the user preferences to get those import/export formats to appear).

This can be used in conjunction with the 'Mesh Cache' modifier to play back a sequence of external meshes:



There also appears to be a script to import .obj sequences as well, which tends to be a more common format, found here at BlenderArtists, but I am not  sure of any potential limitations it may have.